Saturation Estimation in Interactive Computer Systems

This paper presents a systematic method for estimating the saturation point of interactive computer systems in an environment of incomplete information (in particular, where per interaction information is unavailable). This method is an improvement over the ad hoc and time-consuming iterative approach commonly used. Following an operational analysis approach and using only commonly available data, a simple model was constructed to estimate the mean response time of a task characterized by its CPU and i/o requests running in a given system CPU, disk, drum and channel load factors. The systems saturation point is obtained from the model using a modified version of the method first proposed by Kleinrock. The interesting concept that tasks with different resource demands experience different saturation loads is discussed. It is shown that the saturation loads as seen by different tasks vary only slightly as the characteristics of the tasks change. The method has been applied on an IBM 370/168 running under the Michigan Terminal System at the University of British Columbia.